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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Documentation on Delivery Ratio

    used for CEAP Cropland Modeling for

    Various River Basins

    in the United States

    Santhi Chinnasamy1, Xiuying Wang1, Jeff Arnold2,

    Jimmy Williams1, Mike White2, Narayanan

    Kannan1and Mauro Diluzio1

    1Texas AgriLife Research Blackland Research and Extension Center 720 East Blackland Road Temple, TX, 76502

    2USDA-Agricultural Research Service Grassland Soil and Water Research Laboratory 802 East Blackland Road Temple, TX, 76502

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Chapter Organization

    This document describes the delivery ratio procedure used in the CEAP National Assessment for Crop-

    land. The delivery ratio is a factor that compensates for the natural attenuation or loss of sediment and

    nutrients as they travel in water from the source to the watershed outlet. This document covers the deli-

    very ratio procedure used in Soil and Water Assessment Tool (SWAT) and Agricultural Policy Extend-

    er (APEX) models to account for deposition of sediment, nitrogen, phosphorus and atrazine in ditches,

    floodplains, and tributary stream channels during transit from the edge of the field or HRUs to the 8-

    digit watershed outlet. The document is arranged as follows: Chapter 1 covers the development of the

    delivery ratio procedure in APEX and SWAT models and sediment delivery ratio estimated for the Up-

    per Mississippi River basin with several illustrations of the sediment delivery ratio for various types of

    readers/audience from field level to University researchers. Chapters 2 through 5 further describe the

    delivery ratio used in other river basins of the United States by the order of completion. References

    cited in all the Chapters are provided in the Reference Section in Chapter 1.

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Delivery Ratio used in CEAP Cropland

    Modeling in the Upper Mississippi River

    Basin

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Background on Sedimentation and Sediment Delivery Ratio

    Problems caused by soil erosion and sedimentation include losses of soil productivity, water quality degradation, and decreased capacity of channels and reservoirs. Sediment may carry pollutants into water systems and cause signifi-cant water quality problems. Erosion of soil and sediment yield, and subsequent nutrients and pesticides transported with sediment can be strongly impacted by land manage-ment practices, land use and climate changes (Clark et al., 1985). Policy makers need to quantify erosion rates and sediment yields at regional or global levels in order to eva-luate and develop environmental and land use management plans (e.g., COST634, 2005; Mausbach and Dedrick, 2004). The historical record of sediment data is sparse. For example, only a few sediment sampling stations exist in the United Sates and most of the stations have relatively short records (Pannell, 1999). Therefore, reasonable and realistic prediction of sediment yield is important for man-aging natural resources and protecting the environment.

    The methods involving estimating sediment delivery ratios (e.g., Lim et al., 2005; Syvitski et al., 2005; Mutua et al., 2006; Bhattarai and Dutta, 2007) or calculating sediment transport capacity (e.g., Morgan et al., 1998; Van Rom-paey et al., 2001; Vente et at., 2007) are often used to link gross erosion to sediment yield at the watershed outlet. However, not all of the soil that erodes from fields ends up in the watershed outlet. Most of the soil that is eroded gets deposited on the way, although the deposition is tempo-rary. Eroded soil may deposit in low spots, on flatter lands, at the edge of the field and sometimes settles at the bottom of the channel. The delivery ratio is a factor that compen-sates for the natural attenuation or loss of sediment (and nutrients) as they travel in water from the source to the watershed outlet. The processes of transport of sediment from different sources, deposition and re-entrainment on the way to the mouth of a watershed are difficult to model without detailed topographic and small-scale intensive soils and surface condition data. The sediment delivery ratio (SDR) is used as a logical tool to integrate the factors that affect the production of sediment from the gross ero-sion occurring in a watershed. Traditionally, the SDR is defined as the ratio of sediment load delivered to the wa-tershed outlet (sediment yield) to gross erosion occurring from sources within the watershed. Types of erosion in-clude sheet, rill, wind, classic gully, ephemeral gully, streambank, streambed, roadbank and ditch, roadbed, con-

    struction, landslides, and background or geologic erosion. SDR can be affected by a number of factors including hy-drological inputs (rainfall-runoff factors), landscape and watershed characteristics (e.g., land use/land cover, near-ness to the main stream, channel density, drainage area, slope, slope length), soil properties (sediment source, tex-ture) and their interactions. The amount of floodplain se-dimentation occurring and the presence of hydrologically controlled areas (such as ponds, reservoirs, lakes, wet-lands, etc.) also affect the rate of sediment delivery to the watershed mouth and hence the SDR. These complexities make the SDR regionalization mainly empirical. Numer-ous SDR relationships have been developed based on combinations of these factors (Ouyang and Bartholic, 1997). Sediment delivery ratios have also been developed based on measured rates of sediment accumulations in re-servoirs. The types of erosion occurring in a contributing watershed provide information on the relative SDR, when the measured sedimentation rates are also known.

    Sediment delivery ratios are used mostly in planning small to medium water resources projects. Historically one of the most important applications was the NRCS flood con-trol program that involved planning, designing, and eva-luating flood water retarding structures. Traditionally, de-livery ratios have been estimated by comparing sediment yield data with predicted gross erosion. These delivery ratios have been related to watershed characteristics to de-velop delivery ratio prediction equations for use on un-gaged watersheds (Gottschalk and Brune 1950; Maner 1958; Maner 1962; Roehl 1962; Williams and Berndt 1972). However, these analyses depend on the existence of long periods of sediment yield records at the stream gaging stations and; therefore, were limited to a few re-gions of the United States because of insufficient data. This deficiency was partially overcome by using simulated sediment yields (Williams, 1977) for determining delivery ratios. Long-term average annual sediment yields are di-vided by gross erosion to calculate delivery ratios. These simulated delivery ratios are related to watershed characte-ristics to develop equations for predicting delivery ratios for nearby ungaged watersheds.

    With the development of the Modified Universal Soil Loss Equation (MUSLE) (Williams 1975a) and sediment routing (Williams, 1975b; Williams, 1978) it became ap-parent that one of the most important variables in estimat-ing delivery ratios was the peak runoff rate (qp). The origi-nal sediment routing model (Williams 1975b) routed se-

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    diment from subarea outlets to the watershed outlet as a function of qp0.56, travel time, and median particle size. This concept is used in the Agricultural Policy Environ-mental eXtender (APEX) model (Williams and Izaurralde, 2006). Gassman et al. (2009) have provided a comprehen-sive review of APEX model applications and stated that APEX is one of the few existing models which is capable of simulating flow and pollutant transport routing at the field scale. The APEX model has been chosen as the field-scale modeling tool for the Conservation Effects Assess-ment Project (CEAP).

    The CEAP was initiated to quantify the environmental benefits of conservation practices at the regional/national scale. In CEAP, the edge-of-field effects of the conserva-tion practices implemented on cultivated cropland and land enrolled in the Conservation Reserve Program (CRP) of the watershed were assessed using the field scale model, APEX. The watershed scale model, SWAT (Soil and Wa-ter Assessment Tool) was used to simulate the non-cultivated land including pasture, range, urban, forest and wetlands and point sources in the watershed. The results from the APEX model simulations were integrated into the regional water quality model—SWAT (Arnold, et al., 1998; Arnold, et al., 1999; Arnold and Fohrer, 2005)—to assess the off-site effects of conservation practices at re-gional level (Santhi et al., 2005). Gassman et al., (2007) have provided a comprehensive review of SWAT model applications across United States and other countries and recommended SWAT as one of the widely used watershed models with expanding modeling capabilities.

    Databases and model inputs required for SWAT in CEAP is derived from a framework called, HUMUS (Hydrologic Unit Modeling of the United States). In HUMUS/SWAT system, each major river basin in the United States is treated as a watershed and each 8-digit watershed as a subwatershed or subbasin (Figure 1-1). At the 8-digit wa-tershed level, two simulation models, APEX and SWAT, were run independently. The cultivated area estimates were made via a sampling and APEX modeling approach. The simulated results (flow, sediment, nutrients and pesti-cides) from APEX were aggregated to the 8-digit wa-tershed using the statistical sampling weights derived from the National Resource Inventory (NRI) data. The delivery ratio and upland sediment yields were estimated separately for cultivated land and non-cultivated land uses. The inte-grated modeling results at the 8-digit watershed outlets were routed downstream through the stream network along with point sources in SWAT for estimating the offsite ef-

    fects of conservation practices on water quality at the wa-tershed outlets.

    Chapter 1 describes the SDR procedure used in APEX and HUMUS/SWAT models for the CEAP National Assess-ment in the Upper Mississippi River Basin. This chapter includes a discussion of the following:

    1. Development of SDR procedure used for estimating sediment losses (deposition) from edge-of-field to 8-digit watershed outlet in APEX for cultivated cropland and CRP;

    2. Development of SDR procedure used for estimating sediment losses (deposition) from non-cultivated crop-land HRUs to 8-digit watershed outlet in SWAT;

    3. Application and validation of the SDR procedure in the Upper Mississippi River Basin; and

    4. Delivery ratio of sediment bound (organic) and soluble nutrients and pesticides

    For CEAP, at the 8-digit watershed level, there are typical-ly 20 plus NRI-CEAP points simulated with APEX. Each APEX simulation represents a fraction of the cultivated areas by statistical weights assigned to each point. There are about 30-40 hydrologic resource units (HRUs) simu-lated with SWAT. Each HRU represents a particular land use/soil combination, which is a portion of the 8-digit wa-tershed area and does not represent a contiguous land area. Therefore, both the APEX-simulated-cultivated land and SWAT-simulated-HRUs are assumed randomly distributed within the 8-digit watershed.

    Both APEX and SWAT compute SDR as a function of the ratio of time of concentration of the field or HRU to the time of concentration of the 8-digit watershed. As pre-viously described, SDRs are typically defined as the ratio of sediment yield to erosion (soil loss). It is to be noted that delivery ratio estimated for the CEAP national as-sessment is different from the traditionally estimated SDR. In the CEAP national assessment, the SDRs are estimated within each simulation and defined as the ratio of edge-of-field sediment delivered to the 8-digit watershed outlet to the sediment load simulated at APEX sites or SWAT-simulated-HRUs. APEX and SWAT models estimate the sediment yield from the randomly distributed APEX sub-areas and SWAT HRUs to the outlet of the 8-digit wa-tershed or subbasin.

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-1. Major River Basins and 8-digit watersheds in the United States

    Development of delivery ratio from APEX sites to 8-digit watershed outlets The APEX modeling setup for CEAP used information from the NRI-CEAP Cropland Survey. The survey was conducted at a subset of NRI sample points which provide statistical samples representing the diversity of soils and other conditions on the landscape. Since each APEX simu-lation represents a fraction of the cultivated areas within an 8-digit watershed, the actual locations are not known and are assumed to be randomly distributed. Due to this limita-tion, the development of SDR in this study depends on the efficiency of the algorithm with a modest input parameter requirement. The SDR can be estimated as:

    YSDR = B (1)

    ∑YS where YB is the sediment yield at the basin outlet and YS is the sediment yield at the outlet of the APEX sites (or edge-of-field sites). The field surrounding each NRI sample point for modeling purposes, is assumed to be 16 ha, and may be broken into a maximum of four apex subareas, de-pending on the presence of buffer areas or grassed water-ways. Edge-of-field sediment yield (Y) can be estimated using a variation of MUSLE called MUST (MUSLE de-veloped from Theory (Williams 1995):

    αY = 2.5×(Q× q p ) × K ×C × P × LS ×CFRG (2)

    where Q is the runoff volume (mm), qp is the peak runoff rate (mm h-1) , K, C, P, and LS are the linear USLE fac-tors, CFRG is the coarse fragment factor and α is the ru-noff and peak runoff rate exponent, which is set as 0.5 in the original MUST equation (Williams 1995). The α can be smaller than 0.5 in developing the delivery ratio. YB can be calculated with Eq. 2 by areally weighting the linear USLE factors and Q, and estimating qp at the basin outlet. YS can be estimated for each of the APEX sites using ap-propriate values of the linear USLE factors, Q, and qp. The delivery ratio can be estimated by substituting these values into Eq. 1. Since the linear USLE factors and Q cancel, the delivery ratio for each APEX site can be estimated with the equation:

    ⎛ q ⎞α

    SDRS = ⎜ pB ⎟ (3)⎜ ⎟q⎝ pS ⎠

    where SDRS is the delivery ratio for the APEX sites, qpB is the peak runoff rate at the basin outlet (mm h-1), and qpS is

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    the peak runoff rate at the outlet of the APEX sites (mm h-1).

    Since the APEX simulation results are passed to SWAT at the basin outlet, qpB is not known when APEX is running. However, the peak runoff rate is a function of runoff vo-lume and watershed time of concentration:

    ⎛ Q ⎞ qp = f ⎜⎜ ⎟⎟ (4)t⎝ c ⎠

    Substituting the inverse of tc for qp (Q cancels) in Eq 3 yields:

    ⎛ t ⎞α

    SDRS = ⎜⎜ cS ⎟⎟ (5)t⎝ cB ⎠

    where tcS is the time of concentration of the APEX site and tcB is the time of concentration of the basin. The times of concentration can be estimated with the Kirpich equation in the metric form:

    L0.77 t = 0.0663 × (6)c 0.385S where L is the watershed length along the main stem from the outlet to the most distant point (km) and S is the main stem slope (m/m).

    Substituting tcS and tcB calculated from Eq. 6 in Eq. 5 yields:

    0.77 0.385⎛ ⎞α

    ⎛ L ⎞ ⎛ S ⎞⎜ S B ⎟SDRS = ⎜⎜ ⎟⎟ ×⎜⎜ ⎟⎟ (7)⎜ L S ⎟⎝ B ⎠ ⎝ S ⎠⎝ ⎠ where LB and SB are the 8-digit watershed basin channel length (km) and basin channel slope (m/m), respectively; LS and SS are the APEX watershed length (km) and slope (m/m), respectively. Theα was set to 0.2.

    Description of the delivery ratio procedure developed within SWAT SWAT simulates the sediment yield from the non-cultivated land HRUs using the Modified Universal Soil Loss Equation developed by Williams et al. (1975a and 1975b; Williams et al., 1995):

    0.56sed = 11.8 ⋅ (Q ⋅ q ⋅ area ) ⋅ K ⋅ C ⋅ P ⋅ LS ⋅ CFRG (12)surf peak hru USLE USLE USLE USLE

    where sed is the sediment load on a given day (metric tons), Qsurf is the surface runoff volume (mm), qpeak is the peak runoff rate (m3/s), areahru is the area of the HRU (ha), KUSLE is the USLE soil erodibility factor, CUSLE is the USLE cover and management factor, PUSLE is the USLE support practice factor, LSUSLE is the USLE topographic

    factor and CFRG is the coarse fragment factor (Neitsch et al., 2005). The area of each HRU for various land use classes may vary from a few hundred acres to several thousands of acres within each 8-digit watershed.

    After estimating the sediment load for each HRU, a deli-very ratio is applied to determine the amount of sediment that reaches the 8-digit watershed (HUC) outlet from each HRU. In SWAT, SDR is estimated as a function of the time of concentration of HRU to the time of concentration of the HUC/8-digit watershed. Time of concentration is related to watershed characteristics such as slope, slope length, landscape characteristics and drainage area:

    dr _ exp⎛ t ⎞ c,hruSDR = ⎜ ⎟ (13)⎜ ⎟t⎝ c,sub ⎠

    where tc,hru is the time of concentration of HRU in hours, tc,sub is the time of concentration of the subbasin (8-digit HUC) in hours, typically more than 24 hours for most of the 8-digit watersheds, and dr exp is the delivery ratio ex-ponent parameter. Time of concentration of HRU and of 8-digit also varies across the 8-digit watersheds. For the CEAP national assessment, the delivery ratio exponent (dr exp) was set to 0.5 in SWAT. This parameter is similar to the peak runoff rate exponent (α ) used in the MUSLE.

    Computation of time of concentration of subbasin/HUC The time of concentration is calculated by summing the overland flow time (the time it takes for flow from the most remote point in the subbasin to reach the channel) and the channel flow time (the time it takes for flow in the upstream channels to reach the outlet). Total time of con-centration is the sum of overland and channel flow times:

    t c , sub = t + tch , sub (14) ov

    where tc,sub is the time of concentration for a subbasin (hr), tov is the time of concentration for overland flow (hr), and tch,sub is the time of concentration for channel flow (hr).

    Computation of time of concentration of overland flow Tributary channel characteristics related to the HRU such as average slope length (m), HRU slope steepness (m m-1) and Manning’s “n” values representing roughness coeffi-cient for overland flow are used in computing overland flow time of concentration:

    0.6 0.6L ⋅ n t = slp (15)ov 0.318 ⋅ slp

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    where Lslp is the average subbasin slope length (m), slp is the average slope of HRU in the subbasin (m m-1), and n is Manning’s roughness coefficient for the overland flow representing characteristics of the land surface with resi-due cover or tillage operations. Manning’s ”n” ranges from 0.01 to 0.60.

    Computation of time of concentration of channel flow of subbasin The time of concentration for channel flow of the subbasin is computed as:

    0.62 ⋅ L ⋅ n0.75 t = (16)ch,sub 0.125 0.375Sub _ area ⋅ slpch

    where tch,sub is the time of concentration for channel flow (hr), L is the channel length from the most distant point to the subbasin/HUC outlet (km) or the longest tributary channel length, n is Manning’s roughness coefficient for the channel representing the characteristics of the channel (ranges from 0.025 through 0.100), Sub_area is the subba-sin/HUC area (km2), and slpch is the average slope of the longest tributary channel (m m-1).

    Computation of time of concentration of the HRU The time of concentration of HRU is estimated using the following equation.

    t c , hru = t ov + t ch , hru (17)

    Computation of time of concentration of channel flow of HRU The time of concentration for channel flow of the HRU is computed as:

    0.62 ⋅ L * hru _ prop ⋅ n0.75 t = (18)ch,hru 0.3750.125hru _ area ⋅ slpch

    where, hru_prop is the proportion of the tributary channel length in hru. It is estimated by multiplying the longest tributary channel length by the ratio of hru area to subbasin area, and hru_area is the area of hru.

    Equations 15 and 18 are used in computing time of con-centration for HRU as in shown in Eq. 17. Thus, Eqs. 14 and 17 are used in Eq. 12 to compute the SDR. Figure 1-2. depicts the schematic of sediment sources and delivery as modeled with HUMUS/SWAT for the CEAP Cropland National Assessment.

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-2. Schematic of sediment sources and delivery as modeled with HUMUS/SWAT and APEX for the CEAP Crop-land National Assessment

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Application and validation of sediment routing ra-tio procedures The delivery ratio procedures described above have been applied to the CEAP national assessment study in the Up-per Mississippi River Basin (UMRB) (Figure 1-3). The UMRB covers about 190,000 square miles, including large parts of Illinois, Iowa, Minnesota, Missouri, and Wiscon-sin, and small areas of Indiana, Michigan, and South Da-kota. The total cultivated cropland and land enrolled in the CRP General Signup is about 52 percent of the total UMRB area. In most basins, the percent of CRP land is generally less. Most of the cultivated land is located in Iowa, Illinois and Wisconsin. A total of 131 8-digit water-sheds are in the UMRB. Within each 8-digit watershed, the percent cultivated cropland and CRP area ranges from 0 to 89 percent. A total of 5534 representative cultivated fields (3703 NRI-CEAP cropland points and 1831 CRP points) were setup to run using APEX. The statistical weights associated with each representative field range from 6 to 1,369 thousand acres. Nine out of 131 8-digit watersheds in the UMRB have no CEAP points. These nine 8-digit watersheds have zero or fewer than 3 percen-tage cultivated cropland. Non-cultivated land is distributed over 4 percent of the UMRB. Within each 8-digit wa-tershed, non-cultivated land uses such as pasture, range, hay, horticulture, forest deciduous, forest mixed, forest evergreen, urban, urban construction, barren land wetland and water are simulated as HRUs in SWAT. A total of 4452 HRUs are simulated in the Upper Mississippi River Basin.

    Cultivated cropland and CRP Each NRI-CEAP point and CRP point is unique; therefore, sediment yield and delivery ratios also vary for each culti-vated cropland site simulated in an 8-digit watershed. Ex-amples of inputs and the corresponding estimated delivery ratios are listed in Table 1-1. Examples of delivery ratio distributions at the 8-digit watershed level are shown in Figure 1-4. The mean delivery ratios for each of the 8-digit watershed in the UMRB range from 0.30 to 0.46 (Figure 1-5 and Table 1-2).

    Non-cultivated land Since the runoff, tributary channel characteristics, HRU areas, and HUC area vary, sediment yield and delivery ratio also vary for each non-cultivated HRU simulated in an 8-digit watershed. Example inputs used and correspond-ing time of concentrations and delivery ratios for non-cultivated land HRUs are shown for three 8-digit water-sheds in Central Minnesota, Central Iowa and Eastern Missouri near St. Louis (Table 1-3). Figure 1-6 depicts the

    distribution of SDR of non-cultivated land HRUs in those three 8-digit watersheds. Sediment delivery ratio varied from 0.16 to 0.46 depending on the HRU area, slope, slope length, land use characteristics and soil characteristics.

    Figure 1-7 depicts the SDR estimated for major non-cultivated landuses such as forest, urban land, pasture, range grass, hay and urban construction HRUs in each 8-digit watershed in the Upper Mississippi River Basin. Since the SWAT HRU areas are morewidely varied than the areas used in APEX simulation sites (16 ha), the SDR is also varied for some of the pasture, forest and urban land HRUs. Sediment delivery ratios were less for urban con-struction HRUs as their areas are relatively smaller. The MUSLE equation used in SWAT accounts for the area and thus, sediment load predicted by MUSLE per area is lower as HRU area increases. Figure 1-8 depicts the distribution of SDRs for pasture, range grasses, forest, urban and urban construction HRUs in the Upper Mississippi River Basin.

    Table 1-4. shows the mean SDR, 10th percentile and 90th percentile for the non-cultivated land HRUs in all 8-digit watersheds in the Upper Mississippi River Basin. Spatial variation of mean SDR estimated for non-cultivated land HRUs in 8-digit watersheds in the Upper Mississippi River basin is shown in Figure 1-9. The mean delivery ratio va-ried from 0.24 to 0.43across the 8-digit watersheds.

    Validation of sediment delivery ratios used in the Upper Mississippi River Basin Sediment delivery ratio was used in APEX and SWAT models to account for deposition of sediment in ditches, floodplains, and tributary stream channels during transit from the edge of the field to the 8-digit watershed outlet. The SDRs were used to estimate the sediment losses or deposition from each of the cropland APEX simulation sites and non-cropland HRUs to the 8-digit watershed out-lets. The mean SDRs were calculated from the SDRs of APEX sites and SWAT HRUs within each 8-digit wa-tershed. The mean SDR varied from 0.24 through 0.43.

    Meade et al. (1990) developed relationships for sediment yields in the UMRB as a function of drainage area and land use based on a study conducted before 1950. Based on Meade’s relationships, the SDR from the edge-of-fields to the 8-digit watershed outlets is approximately 0.3 to 0.4. Sediment delivery ratios estimated for the upland in the CEAP national assessment study are closer to the delivery ratio range suggested by Meade et al. (1990). This indi-cates that the sediment modeling from the CEAP national assessment study are reasonable.

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Delivery ratio used to compute transport of sediment attached nutrients and pesticides from cropland APEX sites to the 8-digit watershed outlets Sediment transported nutrients and pesticides are simu-lated using an enrichment ratio approach:

    YNPB =YNPS × DR× ERTO (8)

    where YNP is the nutrient or pesticide load and ERTO is the enrichment ratio (concentration of nutrient/pesticide in outflow from APEX sites divided by that at the basin out-let). The enrichment ratio is calculated by considering se-diment concentration in the equation:

    2ERTO = b1 ×YSCb (9)

    where YSC is the sediment concentration of the outflow from the APEX sites and b1 and b2 are parameters that can be determined by considering two points in Eq. 9. For the enrichment ratio to approach 1.0, the sediment concentration must be extremely high. Conversely, for the enrichment ratio to approach 1/SDR, the sediment concentration must be low. The simultaneous solution of Eq. 9 at the boundaries assuming that sediment concentrations range from 5x10-4 to 0.1 Mg m-3 gives:

    b2 = log(SDR)/ 2.301 (10) b1 =1/ 0.1

    b2 (11) Thus, the delivery ratios and enrichment ratios are used to transport sediment, nutrients, and pesticides from APEX sites to the basin outlet for input to SWAT.

    Delivery ratio used to compute transport of sediment attached nutrients and pesticides from non-cultivated land HRUs to the 8-digit watershed outlets For non-cultivated land uses simulated within SWAT, or-ganic nitrogen, phosphorus and pesticide transported with sediment are calculated with a loading function developed by McElroy et al. (1976) and modified by Williams and Hann (1978) for application to individual runoff events. The basic concept of the loading function used in SWAT is identical to APEX. The loading function estimates the dai-ly organic N runoff loss from a HRU, based on the concen-tration of organic N or P in the top soil layer in the field or HRU, the sediment yield, and the enrichment ratio. The enrichment ratio (Menzel, 1980) is the concentration of organic nitrogen, phosphorus and pesticide transported with sediment to the main channel to the concentration in the soil surface layer at the field or HRU.

    In addition to the SDR, the enrichment ratio was used to simulate organic nitrogen, organic phosphorus, and sedi-ment-attached pesticide transport in ditches, floodplains, and tributary stream channels during transit from the edge of the field or HRU to the outlet (Menzel, 1980). The enrichment ratio was defined as the organic nitrogen, or-ganic phosphorus, and sediment attached pesticide concen-tration transported with sediment to the watershed outlet divided by their concentration at the edge-of-field. As se-diment is transported from the edge-of-field to the wa-tershed outlet, coarse sediments are deposited first, while more of the fine sediments that hold organic particles re-main in suspension enriching the organic concentrations delivered to the watershed outlet.

    Thus, the edge of loadings of sediment bound nutrients (organic nitrogen and phosphorus) and pesticides delivered to the 8-digit watershed outlets account for the delivery losses based on the SDR and enrichment ratio simulated within APEX model and SWAT models.

    Delivery ratio for soluble nutrients used from cropland and CRP from APEX Loads simulated by APEX for each survey point were ap-propriately weighted to develop a single aggregated load for all cultivated cropland within each 8-digit watershed. Sediment and particulate (organic) nutrients forms are sub-ject to delivery ratios appropriate to their relative source locations within the subbasin and distance to the SWAT subbasin outlet. This adjustment is performed within the APEX prior to the inclusion of APEX loads into SWAT. However, soluble nutrient and pesticide loading from APEX is excluded from this delivery ratio adjustment. To reconcile this discrepancy, delivery ratio for soluble con-stituents were applied to APEX loads within the SWAT model. In this way both soluble and particulate constitu-ents from cultivated cropland are treated with a delivery ratio. In order to fit the existing modeling framework, sep-arate delivery ratios for soluble constituents were needed. Development of delivery ratios for soluble nutrients and pesticides is difficult. In-stream interaction between so-luble and particulate fractions are complex and difficult to isolate, thus there are little research data upon which to base appropriate values. Soluble delivery ratios for APEX loads were derived from in-stream soluble nutrient and pesticide delivery as predicted by SWAT. The SWAT model predicts these losses within each river reach using the routines adapted from the QUAL2E model. The aver-age delivery ratios predicted by SWAT for a single reach

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    segment in the UMRB were 0.97, 0.93 and 0.94 for nitrate, soluble phosphorus and soluble pesticide, respectively. Because they are derived from the SWAT model, soluble loads from non-cultivated areas are already subject to simi-lar reductions. Application of soluble delivery ratios en-sures equitable treatment of pollutants between APEX and SWAT. Individual delivery ratios were calculated using equations (12 to 14) as described below. These values typ-ically ranged from 0.80 to 0.98, indicating in general a higher delivery ratio for soluble as compared to particulate (organic) fractions.

    Development of delivery ratios for soluble nutrients and pesticides is difficult. There is little existing research upon which to base appropriate values. Instream interaction be-tween soluble and particulate fractions make it difficult to isolate delivery ratios for each fraction from measured da-ta, yet in order to fit the existing modeling framework sep-arate delivery ratios are needed. Due to a lack of measured delivery ratios for soluble fractions in the literature, these data were derived from SWAT predictions. Delivery ra-tios applied to the monthly soluble loads from the APEX model were derived from SWAT predicted pollutant reten-tion by reach. The SWAT model predicts the loss of so-luble nutrient and pesticides within each reach due to in-stream processes. These predictions can be used to esti-mate a delivery ratio for soluble fractions for each reach in the model. The average delivery ratios predicted by SWAT for a single reach segment in the UMRB were 0.97, 0.93 and 0.94 for nitrate, soluble phosphorus and soluble pesticide, respectively. Because they are derived from the SWAT model, soluble loads from non-cultivated areas are already subject to similar reductions. To ensure equitable treatment of soluble pollutants between APEX and SWAT, the application of these delivery ratios is needed. Individu-al delivery ratios were calculated using Eq. 12 through 14 as described below. Delivery ratios used for soluble nu-trients and pesticides were greater than 0.9 in most of the basins.

    Nitrate Delivery Ratio

    The nitrate delivery ratio in the main channel reach, NO3_DR_RCH, is calculated as follows:

    NO3_DR_RCH = NO3_OUT_RCH/ NO3_IN_RCH (12)

    where NO3_IN_RCH is the nitrate transported with water into reach and NO3_OUT_RCH is the nitrate transported with water out of reach. NO3_IN_RCH load includes ni-trogen loads accumulated from subbasins above that reach).

    Soluble Phosphorus Delivery Ratio

    MINP_DR_RCH = MINP_OUT_RCH/ MINP_IN_RCH (13)

    where, MINP_DR_RCH is the in-stream mineral phospho-rus delivery ratio in the main channel reach, MINP_IN_RCH is the mineral phosphorus transported with water into reach, and MINP_OUT_RCH is the miner-al phosphorus transported with water out of reach. MINP_IN load includes phosphorus loads accumulated from subbasins above that reach).

    Soluble Pesticide Delivery Ratio

    SOLPST_DR_RCH = SOLPST_OUT_RCH/ SOLPST_IN_RCH (14)

    where, SOLPST_DR_RCH is the instream soluble pesti-cide delivery ratio in the main channel reach, SOLPST_IN_RCH is the soluble pesticide transported with water into reach, and SOLPST_OUT_RCH is the soluble pesticide transported with water out of reach.

    While more than one pesticide may be applied to the HRUs in SWAT, due to the complexity of the pesticide equations only one pesticide is routed through the stream network. Several types of pesticides are applied to crop-land and horticultural land in the Upper Mississippi River Basin. For the CEAP national assessment, atrazine was chosen as one of the high priority or high risk pesticides in the Upper Mississippi River Basin. The only source of atrazine load is cultivated cropland; point sources and non-cultivated land had no atrazine contributions. Atrazine is routed through the stream reach during SWAT simulation. A delivery ratio of 0.94 was chosen soluble pesticides for the UMRB.

    Summary • Sediment delivery ratio is used to account for the

    sediment losses or deposition in ditches, channels, and floodplain occurring from edge-of-field of the cropland or non-cropland HRU to 8-digit wa-tershed outlets in each river basin.

    • Sediment delivery ratio is unique for each culti-vated land and CRP survey point and each non-cultivated cropland HRU. Sediment delivery ratio varied as a function of drainage area, HRU of farm-field area, channel slope, slope length, soil, land use and management factors.

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    • Mean SDR (from edge-of-field to 8-digit wa-tershed outlet SDR) varied from 0.3 to 0.5 for cul-tivated and CRP land simulated within APEX and it varied from 0.21 to 0.45 for non-cultivated land use HRUs simulated within SWAT.

    • Edge-of-field loadings of sediment-bound nu-trients (organic nitrogen and phosphorus) deli-vered to the 8-digit watershed outlets account for the delivery losses based on the SDR and enrich-

    ment ratio simulated within APEX and SWAT models.

    • Soluble nutrient and pesticide delivery ratios were derived from the SWAT instream model and ap-plied to APEX loadings. The application of so-luble nutrient and pesticide delivery ratios to APEX loading ensures equitable treatment of the loads generated for cultivated and non-cultivated areas.

    1-13

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-3 Map of the 8-digit watersheds in the Upper Mississippi River Basin

    1-14

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-4 Examples of sediment delivery ratio distributions for cultivated cropland (edge-of-field to 8-digit wa-tershed outlet) in the Upper Mississippi River Basin

    HUC=07020011 HUC=07040008 HUC=07060006 HUC=07120001 HUC=07140204

    0.3

    0.35

    0.4

    0.45

    0.5

    0.55

    0.3

    0.35

    0.4

    0.45

    0.5

    0.55

    0.3

    0.35

    0.4

    0.45

    0.5

    0.55

    0.3

    0.35

    0.4

    0.45

    0.5

    0.55

    0.3

    0.35

    0.4

    0.45

    0.5

    0.55

    Figure 1-5 Mean sediment delivery ratio (sediment yield at the 8-digit watershed outlet divided by sediment yield at the edge-of-cropland fields) for cultivated cropland in the Upper Mississippi River Basin

    Del

    iver

    y ra

    tio d

    istr

    ibut

    ion

    1-15

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Table 1-1 Examples of inputs and estimated delivery ratios for cultivated cropland in the Upper Mississippi River Basin

    8-digit wa-tershed NO.

    SWAT basin

    channel length

    LB (km)

    SWAT basin channel slope

    SB (m/m)

    APEX site watershed

    length‡ LS (km)

    APEX site main

    stem slope SS (m/m)

    Time of conc.

    of the basin tcB (h)

    Time of conc. of the APEX

    site tcW (h)

    Delivery ratio DRS

    07100009 239.9 0.001 0.447 0.051 64.44 0.11 0.28 0.447 0.016 64.44 0.18 0.31 0.447 0.002 64.44 0.39 0.36

    07020001 92.3 0.003 0.447 0.013 20.23 0.19 0.39 07070006 115.5 0.002 0.447 0.031 28.11 0.14 0.34 07010108 69.5 0.001 0.447 0.017 24.82 0.17 0.37

    ‡ Each APEX site is assumed to be a 16 ha of square area.

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Table 1-2 Sediment delivery ratios for cultivated cropland by 8-digit watershed

    HUC Cropland CRP Crop + CRP

    Points Mean SDR Points Mean SDR Points

    Mean SDR

    10th per-centile

    90th percen-tile

    7010104 4 0.38 4 0.38 0.34 0.49 7010106 8 0.37 3 0.36 11 0.37 0.34 0.41 7010107 5 0.39 2 0.37 7 0.39 0.37 0.40 7010108 5 0.39 14 0.38 19 0.38 0.36 0.43 7010201 10 0.42 1 0.37 11 0.41 0.36 0.53 7010202 13 0.35 9 0.34 22 0.35 0.32 0.39 7010203 16 0.39 4 0.36 20 0.38 0.34 0.47 7010204 25 0.37 30 0.37 55 0.37 0.33 0.40 7010205 24 0.39 3 0.37 27 0.39 0.34 0.49 7010206 11 0.40 11 0.40 0.37 0.44 7010207 18 0.41 18 0.41 0.36 0.50 7020001 41 0.41 38 0.39 79 0.40 0.37 0.43 7020002 10 0.41 6 0.39 16 0.40 0.35 0.50 7020003 35 0.44 23 0.41 58 0.43 0.37 0.55 7020004 35 0.39 24 0.36 59 0.38 0.33 0.44 7020005 31 0.37 36 0.36 67 0.37 0.32 0.46 7020006 17 0.42 17 0.40 34 0.41 0.37 0.48 7020007 24 0.43 3 0.40 27 0.42 0.36 0.51 7020008 32 0.37 4 0.37 36 0.37 0.33 0.40 7020009 38 0.38 2 0.32 40 0.38 0.32 0.46 7020010 17 0.45 4 0.41 21 0.44 0.39 0.50 7020011 30 0.39 10 0.35 40 0.38 0.33 0.45 7020012 34 0.36 6 0.32 40 0.36 0.31 0.41 7030001 3 0.37 3 0.37 0.33 0.44 7030003 1 0.33 1 0.33 0.33 0.33 7030004 7 0.35 7 0.35 0.32 0.37 7030005 28 0.34 17 0.33 45 0.34 0.30 0.37 7040001 35 0.40 13 0.37 48 0.39 0.35 0.45 7040002 76 0.36 30 0.34 106 0.35 0.31 0.44 7040003 20 0.34 11 0.33 31 0.34 0.31 0.37 7040004 62 0.36 16 0.33 78 0.35 0.31 0.38 7040005 13 0.34 13 0.32 26 0.33 0.31 0.37 7040006 9 0.38 7 0.34 16 0.36 0.34 0.41 7040007 14 0.34 3 0.29 17 0.33 0.28 0.37 7040008 85 0.36 40 0.33 125 0.35 0.31 0.41 7050001 1 0.33 1 0.33 0.33 0.33 7050002 1 0.39 1 0.39 0.39 0.39 7050004 1 0.44 1 0.41 2 0.43 0.41 0.44 7050005 23 0.36 6 0.33 29 0.35 0.31 0.38 7050006 5 0.35 2 0.33 7 0.34 0.31 0.38 7050007 20 0.35 16 0.33 36 0.34 0.30 0.36 7060001 17 0.42 34 0.38 51 0.40 0.37 0.43 7060002 34 0.35 32 0.32 66 0.33 0.31 0.37 7060003 26 0.38 35 0.36 61 0.37 0.35 0.40

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    7060004 30 0.33 41 0.30 71 0.31 0.29 0.35 7060005 49 0.41 46 0.36 95 0.38 0.35 0.43 7060006 61 0.32 46 0.29 107 0.31 0.29 0.35 7070002 13 0.37 13 0.37 0.35 0.40 7070003 34 0.34 6 0.29 40 0.33 0.29 0.37 7070004 4 0.37 6 0.33 10 0.35 0.32 0.44 7070005 21 0.34 39 0.31 60 0.32 0.30 0.35 7070006 9 0.36 15 0.34 24 0.34 0.33 0.39 7080101 41 0.39 12 0.36 53 0.39 0.34 0.46 7080102 35 0.36 7 0.33 42 0.36 0.33 0.43 7080103 36 0.37 11 0.32 47 0.35 0.31 0.41 7080104 74 0.39 19 0.35 93 0.38 0.33 0.44 7080105 41 0.35 23 0.32 64 0.34 0.29 0.42 7080106 21 0.34 27 0.32 48 0.33 0.31 0.37 7080107 36 0.37 58 0.31 94 0.33 0.30 0.40 7080201 82 0.36 25 0.35 107 0.36 0.31 0.42 7080202 45 0.39 20 0.38 65 0.39 0.34 0.47 7080203 16 0.40 7 0.39 23 0.40 0.35 0.47 7080204 16 0.39 3 0.35 19 0.38 0.34 0.48 7080205 43 0.34 7 0.30 50 0.34 0.30 0.35 7080206 24 0.40 11 0.35 35 0.39 0.34 0.47 7080207 29 0.36 7 0.34 36 0.36 0.31 0.42 7080208 28 0.36 21 0.32 49 0.35 0.31 0.42 7080209 69 0.36 52 0.32 121 0.34 0.30 0.39 7090001 69 0.36 16 0.32 85 0.35 0.31 0.38 7090002 22 0.40 7 0.37 29 0.39 0.34 0.42 7090003 50 0.34 38 0.31 88 0.33 0.30 0.36 7090004 19 0.37 6 0.33 25 0.36 0.32 0.45 7090005 73 0.36 22 0.32 95 0.35 0.31 0.40 7090006 64 0.39 6 0.36 70 0.39 0.35 0.43 7090007 25 0.38 5 0.35 30 0.38 0.33 0.42 7100001 78 0.39 24 0.37 102 0.39 0.34 0.42 7100002 18 0.39 7 0.36 25 0.38 0.32 0.47 7100003 28 0.40 6 0.39 34 0.40 0.36 0.46 7100004 31 0.39 2 0.39 33 0.39 0.36 0.47 7100005 15 0.41 1 0.37 16 0.41 0.36 0.47 7100006 44 0.34 5 0.31 49 0.34 0.31 0.37 7100007 31 0.39 19 0.33 50 0.37 0.32 0.47 7100008 46 0.34 59 0.31 105 0.32 0.29 0.36 7100009 27 0.32 83 0.30 110 0.30 0.28 0.34 7110001 35 0.35 38 0.32 73 0.34 0.30 0.39 7110002 25 0.35 43 0.32 68 0.33 0.30 0.37 7110003 13 0.38 40 0.34 53 0.35 0.31 0.38 7110004 35 0.40 25 0.37 60 0.39 0.35 0.44 7110005 24 0.35 41 0.33 65 0.34 0.30 0.37 7110006 33 0.39 52 0.36 85 0.37 0.34 0.39

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    7110007 19 0.40 29 0.38 48 0.39 0.36 0.42 7110008 30 0.36 15 0.33 45 0.35 0.32 0.39 7110009 21 0.41 6 0.37 27 0.40 0.35 0.47 7120001 71 0.38 4 0.32 75 0.38 0.33 0.43 7120002 56 0.41 4 0.37 60 0.41 0.35 0.48 7120003 3 0.46 3 0.46 0.40 0.50 7120004 15 0.41 3 0.39 18 0.41 0.37 0.45 7120005 26 0.41 2 0.35 28 0.41 0.35 0.47 7120006 41 0.34 9 0.33 50 0.34 0.30 0.37 7120007 49 0.39 2 0.34 51 0.38 0.34 0.46 7130001 53 0.35 1 0.31 54 0.35 0.32 0.36 7130002 38 0.40 3 0.40 41 0.40 0.36 0.48 7130003 35 0.42 6 0.40 41 0.42 0.37 0.47 7130004 22 0.37 6 0.33 28 0.36 0.32 0.40 7130005 54 0.35 6 0.32 60 0.35 0.30 0.39 7130006 33 0.36 1 0.35 34 0.36 0.32 0.41 7130007 21 0.42 1 0.34 22 0.41 0.36 0.48 7130008 26 0.43 7 0.37 33 0.42 0.34 0.51 7130009 39 0.37 1 0.32 40 0.37 0.33 0.42 7130010 41 0.37 4 0.32 45 0.37 0.32 0.40 7130011 66 0.39 12 0.35 78 0.38 0.34 0.43 7130012 24 0.37 4 0.33 28 0.37 0.32 0.42 7140101 24 0.42 3 0.36 27 0.41 0.36 0.47 7140103 4 0.38 4 0.38 0.36 0.43 7140105 30 0.40 20 0.35 50 0.38 0.34 0.48 7140106 47 0.36 48 0.34 95 0.35 0.31 0.41 7140107 5 0.41 9 0.36 14 0.38 0.34 0.44 7140108 18 0.45 19 0.37 37 0.41 0.36 0.53 7140201 40 0.38 4 0.33 44 0.37 0.33 0.42 7140202 45 0.38 17 0.35 62 0.37 0.33 0.43 7140203 31 0.40 12 0.36 43 0.39 0.35 0.44 7140204 50 0.36 4 0.37 54 0.36 0.32 0.42

    1-19

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-6 Examples of sediment delivery ratio distributions for non-cultivated land HRUs for three 8-digit watersheds in the Upper Mississippi River Basin

    HUC=7030003 HUC=7100004 HUC=7110008

    (Central Minnesota) (Central Iowa) (East Central Missouri)

    1-20

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-7 Sediment delivery ratio estimated for major non-cultivated land HRUs (Forest, Pasture, Range, Urban and Construction) in the Upper Mississippi River Basin

    1-21

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-7 Sediment delivery ratio estimated for major non-cultivated land HRUs (Forest, Pasture, Range, Urban and Construction) in the Upper Mississippi River Basin (Contd.)

    1-22

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  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-8 Distribution of sediment delivery ratio for forest, urban, pasture, range and construction HRUs in the Upper Mississippi River Basin

    Distribution for Forest Deciduous Distribution for Urban Land Distribution for Pasture Land

    Forest Deciduous Urban Land Pasture Land

    100.0% maximum 0.68 99.5% 0.62 97.5% 0.51 90.0% 0.42 75.0% Quartile 0.35 50.0% Median 0.30 25.0% Quartile 0.26 10.0% 0.23 2.5% 0.19 0.5% 0.16 0.0% minimum 0.12

    100.0% maximum 99.5% 97.5% 90.0% 75.0% quartile 50.0% median 25.0% quartile 10.0% 2.5% 0.5% 0.0% minimum

    0.67 0.64 0.55 0.46 0.39 0.33 0.28 0.24 0.21 0.18 0.17

    100.0% maximum 99.5% 97.5% 90.0% 75.0% quartile 50.0% median 25.0% quartile 10.0% 2.5% 0.5% 0.0% minimum

    0.51 0.48 0.43 0.37 0.33 0.28 0.24 0.21 0.15 0.12 0.10

    Moments for Forest Deciduous

    Mean 0.31 Std Dev 0.08 Std Err Mean 0.00 upper 95% Mean 0.32 lower 95% Mean 0.31 N 848

    Moments for Urban land

    Mean Std Dev Std Err Mean upper 95% Mean lower 95% Mean N

    0.34 0.08 0.00 0.35 0.33 521

    Moments for Pasture land

    Mean Std Dev Std Err Mean upper 95% Mean lower 95% Mean N

    0.29 0.07 0.00 0.29 0.28 450

    1-23

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-8 Distribution of sediment delivery ratio for forest, urban and pasture land HRUs in the Upper Mississippi River Basin Continued.

    Distribution for Range Grasses Distribution for Urban Construction

    Range Grasses Urban Construction

    100.0% Maximum 0.70 100.0% maximum 0.23 99.5% 0.70 99.5% 0.23 97.5% 0.53 97.5% 0.18 90.0% 0.48 90.0% 0.17 75.0% Quartile 0.42 75.0% quartile 0.16 50.0% Median 0.32 50.0% median 0.13 25.0% Quartile 0.25 25.0% quartile 0.10 10.0% 0.22 10.0% 0.09 2.5% 0.19 2.5% 0.08 0.5% 0.17 0.5% 0.08 0.0% Minimum 0.17 0.0% minimum 0.08 Moments for Range Grasses Moments for Construction

    Mean 0.34 Mean 0.13 Std Dev 0.10 Std Dev 0.03 Std Err Mean 0.01 Std Err Mean 0.00 upper 95% Mean 0.35 upper 95% Mean 0.13 lower 95% Mean 0.32 lower 95% Mean 0.12 N 141 N 132

    1-24

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Figure 1-9 Mean sediment delivery ratio computed for non-cultivated land HRUs in the 8-digit watersheds in the Upper Mississippi River Basin

    1-25

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Table 1-3 Example inputs, time of concentration and sediment delivery ratio estimated for non-cultivated land HRUs in three 8-digit watersheds in the Upper Mississippi River Basin

    HUC Landuse

    Time of

    conc. of

    HRU

    Time of

    conc. of sub-basin

    Delivery Ratio

    Area (ha)

    Subbasin Slope

    Length (km)

    Subba-sin

    Chan-nel

    Slope (%)

    HRU Slope

    %

    HRU Slope

    Length (m)

    7030003 Forest Deciduous 3.75 44.84 0.29 8189.06 97.45 0.001 0.006 149.49 7030003 Forest Deciduous 5.36 46.24 0.34 9156.76 97.45 0.001 0.003 291.43 7030003 7.42 46.24 0.40 19020.22 97.45 0.001 0.003 291.43 7030003 Forest Deciduous 5.59 47.55 0.34 4438.21 97.45 0.001 0.002 430.65 7030003 Forest Deciduous 3.64 45.56 0.28 4613.28 97.45 0.001 0.004 220.9 7030003 Forest Deciduous 4.23 45.56 0.31 7154.59 97.45 0.001 0.004 220.9 7030003 Forest Deciduous 3.14 45.13 0.26 4286.86 97.45 0.001 0.005 178.18 7030003 Forest Deciduous 2.86 45.13 0.25 3162.41 97.45 0.001 0.005 178.18 7030003 Pasture 2.48 44.84 0.24 2806.13 97.45 0.001 0.006 149.49 7030003 Forest Deciduous 3.45 44.84 0.28 6871.12 97.45 0.001 0.006 149.49 7030003 Water 3.07 44.84 0.26 5225.95 97.45 0.001 0.006 149.49 7030003 Pasture 3.26 45.56 0.27 3070.57 97.45 0.001 0.004 220.9 7030003 Forest Deciduous 5.47 45.56 0.35 12834.84 97.45 0.001 0.004 220.9 7030003 Range Brush 3.48 46.24 0.28 1314.22 97.45 0.001 0.003 291.43 7030003 Forest Deciduous 5.81 46.24 0.35 11212.00 97.45 0.001 0.003 291.43 7030003 Evergreen Forest 6.25 46.24 0.37 13286.06 97.45 0.001 0.003 291.43

    7030003 Non-forested wet-land 4.75 46.24 0.32 6446.94 97.45 0.001 0.003 291.43

    7030003 Forest Deciduous 3.76 44.84 0.29 8210.15 97.45 0.001 0.006 149.49 7030003 Horticulture 2.41 45.56 0.23 63.49 97.45 0.001 0.004 220.9 7030003 Legume Hay 4.45 45.56 0.31 8140.74 97.45 0.001 0.004 220.9 7030003 Other Hay 3.31 45.56 0.27 3274.88 97.45 0.001 0.004 220.9 7030003 Pasture 4.56 45.56 0.32 8626.58 97.45 0.001 0.004 220.9

    7030003 Pasture with ma-nure 2.43 45.56 0.23 125.58 97.45 0.001 0.004 220.9

    7030003 Range Grass 5.39 45.56 0.34 12454.14 97.45 0.001 0.004 220.9 7030003 Forest Deciduous 7.46 45.56 0.41 22695.27 97.45 0.001 0.004 220.9 7030003 Forest Mixed 2.51 45.56 0.24 338.62 97.45 0.001 0.004 220.9 7030003 Urban 4.64 45.56 0.32 8984.70 97.45 0.001 0.004 220.9

    7030003 Non-forested wet-land 5.07 45.56 0.33 10980.90 97.45 0.001 0.004 220.9

    7030003 Legume Hay with Manure 2.39 45.56 0.23 15.81 97.45 0.001 0.004 220.9

    7030003 Other Hay with Manure 2.41 45.56 0.23 52.87 97.45 0.001 0.004 220.9

    7030003 Urban Construction 0.34 43.40 0.09 277.87 97.45 0.001 0.15 6.73 7030003 Pasture 3.49 45.13 0.28 5757.54 97.45 0.001 0.005 178.18

    7030003 Deciduous Forest 6.05 45.13 0.37 17695.35 97.45 0.001 0.005 178.18

    7030003 Non-forested wet-land 3.96 45.13 0.30 7838.74 97.45 0.001 0.005 178.18

    1-26

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    7030003 Deciduous Forest 4.08 46.24 0.30 3595.33 97.45 0.001 0.003 291.43 7030003 Deciduous Forest 4.95 45.56 0.33 10414.63 97.45 0.001 0.004 220.9 7030003 Barren 2.39 45.56 0.23 13.79 97.45 0.001 0.004 220.9

    7030003 Non-forested wet-land 4.20 45.56 0.30 7011.85 97.45 0.001 0.004 220.9

    7030003 Deciduous Forest 3.69 46.24 0.28 2065.97 97.45 0.001 0.003 291.43

    7100004 Urban 7.68 52.82 0.38 4867.44 97.5 0.001 0.002 430.65 7100004 Barren 8.36 56.49 0.39 344.09 97.5 0.001 0.001 839.55 7100004 Urban 11.31 56.49 0.45 4822.25 97.5 0.001 0.001 839.55 7100004 Deciduous Forest 8.25 49.62 0.41 11641.30 97.5 0.001 0.009 101.16 7100004 Range Grass 7.40 49.74 0.39 9810.96 97.5 0.001 0.008 113.31 7100004 Deciduous Forest 10.54 49.74 0.46 15780.72 97.5 0.001 0.008 113.31

    7100004 Evergreen Forest 1.36 49.74 0.17 49.35 97.5 0.001 0.008 113.31

    7100004 Urban 5.55 49.74 0.33 6500.42 97.5 0.001 0.008 113.31

    7100004 Non-forested wet-land 2.74 49.74 0.24 1893.58 97.5 0.001 0.008 113.31

    7100004 Horticulture 1.92 50.11 0.20 251.88 97.5 0.001 0.006 149.49 7100004 Legume Hay 3.77 50.11 0.27 2901.51 97.5 0.001 0.006 149.49 7100004 Other Hay 2.40 50.11 0.22 867.17 97.5 0.001 0.006 149.49 7100004 Pasture 7.05 50.11 0.38 8509.06 97.5 0.001 0.006 149.49

    7100004 Pasture with ma-nure 1.71 50.11 0.19 32.91 97.5 0.001 0.006 149.49

    7100004 Range Grass 1.68 50.11 0.18 5.93 97.5 0.001 0.006 149.49 7100004 Urban 10.58 50.11 0.46 15124.34 97.5 0.001 0.006 149.49 7100004 Forested Wetland 4.38 50.11 0.30 3882.58 97.5 0.001 0.006 149.49

    7100004 Legume Hay with Manure 1.68 50.11 0.18 9.80 97.5 0.001 0.006 149.49

    7100004 Other Hay with Manure 1.69 50.11 0.18 15.54 97.5 0.001 0.006 149.49

    7100004 Urban Construction 1.26 48.67 0.16 1282.71 97.5 0.001 0.15 6.73 7100004 Water 5.27 49.74 0.33 6020.68 97.5 0.001 0.008 113.31

    7100004 Mixed Forest

    1.46 49.90 0.17 0.94 97.5 0.001 0.007 128.86 7100004 Urban 7.75 49.90 0.39 10159.64 97.5 0.001 0.007 128.86 7110008 Pasture 3.28 57.89 0.24 8189.06 121.08 0.001 0.006 149.49 7110008 Pasture 4.68 58.18 0.28 9156.76 121.08 0.001 0.005 178.18 7110008 Deciduous Forest 5.43 58.18 0.31 19020.22 121.08 0.001 0.005 178.18 7110008 Pasture 3.52 57.39 0.25 4438.21 121.08 0.001 0.009 101.16 7110008 Deciduous Forest 4.30 57.39 0.27 4613.28 121.08 0.001 0.009 101.16 7110008 Pasture 4.77 59.29 0.28 7154.59 121.08 0.001 0.003 291.43 7110008 Horticulture 2.12 58.18 0.19 4286.86 121.08 0.001 0.005 178.18 7110008 Legume Hay 3.83 58.18 0.26 3162.41 121.08 0.001 0.005 178.18 7110008 Other Hay 7.40 58.18 0.36 2806.13 121.08 0.001 0.005 178.18 7110008 Pasture 5.41 58.18 0.31 6871.12 121.08 0.001 0.005 178.18 7110008 Pasture with Ma-

    nure 2.10 58.18 0.19 5225.95 121.08 0.001 0.005 178.18

    7110008 Deciduous Forest 8.34 58.18 0.38 3070.57 121.08 0.001 0.005 178.18 7110008 Urban 4.25 58.18 0.27 12834.84 121.08 0.001 0.005 178.18

    1-27

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    7110008 Forested Wetland 4.65 58.18 0.28 1314.22 121.08 0.001 0.005 178.18 7110008 Water 2.80 58.18 0.22 11212.00 121.08 0.001 0.005 178.18 7110008 Legume Hay with

    Manure 1.97 58.18 0.18 13286.06 121.08 0.001 0.005 178.18

    7110008 Other Hay with Manure

    2.09 58.18 0.19 6446.94 121.08 0.001 0.005 178.18

    7110008 Pasture 2.89 57.29 0.23 8210.15 121.08 0.001 0.01 91.4 7110008 Forest Deciduous 5.37 57.29 0.31 63.49 121.08 0.001 0.01 91.4 7110008 Pasture 3.20 58.18 0.23 8140.74 121.08 0.001 0.005 178.18 7110008 Forest Deciduous 3.76 58.18 0.25 3274.88 121.08 0.001 0.005 178.18 7110008 Pasture 3.70 57.68 0.25 8626.58 121.08 0.001 0.007 128.86 7110008 Forest Deciduous 5.88 57.68 0.32 125.58 121.08 0.001 0.007 128.86 7110008 Barren 1.67 57.68 0.17 12454.14 121.08 0.001 0.007 128.86 7110008 Urban 3.72 57.68 0.25 22695.27 121.08 0.001 0.007 128.86 7110008 Pasture 3.49 58.60 0.24 338.62 121.08 0.001 0.004 220.9 7110008 Pasture 2.17 57.39 0.19 8984.70 121.08 0.001 0.009 101.16 7110008 Forest Deciduous 4.06 57.39 0.27 10980.90 121.08 0.001 0.009 101.16 7110008 Forest Deciduous 4.59 57.89 0.28 15.81 121.08 0.001 0.006 149.49 7110008 Pasture 4.37 57.68 0.28 52.87 121.08 0.001 0.007 128.86 7110008 Range Brush 1.62 57.68 0.17 277.87 121.08 0.001 0.007 128.86 7110008 Range Grass 2.87 57.68 0.22 5757.54 121.08 0.001 0.007 128.86 7110008 Forest Deciduous 9.36 57.68 0.40 17695.35 121.08 0.001 0.007 128.86 7110008 Evergreen Forest 1.75 57.68 0.17 7838.74 121.08 0.001 0.007 128.86 7110008 Mixed Forest 1.63 57.68 0.17 3595.33 121.08 0.001 0.007 128.86 7110008 Urban 3.91 57.68 0.26 10414.63 121.08 0.001 0.007 128.86 7110008 Urban Construction 0.57 56.45 0.10 13.79 121.08 0.001 0.15 6.73 7110008 Pasture 3.16 57.89 0.23 7011.85 121.08 0.001 0.006 149.49 7110008 Forest Deciduous 3.54 57.89 0.25 2065.97 121.08 0.001 0.006 149.49 7110008 Urban 3.16 57.89 0.23 8189.06 121.08 0.001 0.006 149.49 7110008 Non-forested Wet-

    land 1.77 57.89 0.18 9156.76 121.08 0.001 0.006 149.49

    1-28

  •                      

     

    Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    Table 1-4. Mean and percentiles of sediment delivery ratio (sediment delivered at 8-digit watershed outlet by sediment yield at HRUs) estimated for non-cultivated land HRUs within SWAT for the 8-digit watersheds in the Upper Mississippi River Basin

    HUC Subbasin

    Number_of non-cropland HRUs simulated within SWAT Mean SDR

    10th Percentile SDR

    90th Percentile SDR

    7010101 1 41 0.31 0.25 0.38 7010102 2 36 0.28 0.21 0.39 7010103 3 40 0.31 0.24 0.37 7010104 4 42 0.32 0.25 0.39 7010105 5 37 0.30 0.24 0.37 7010106 6 41 0.30 0.23 0.36 7010107 7 48 0.30 0.25 0.36 7010108 8 45 0.32 0.26 0.36 7010201 9 49 0.32 0.28 0.39 7010202 10 39 0.26 0.19 0.34 7010203 11 47 0.29 0.24 0.34 7010204 12 33 0.30 0.23 0.40 7010205 13 33 0.30 0.23 0.41 7010206 14 37 0.36 0.30 0.44 7010207 15 45 0.38 0.33 0.43 7020001 16 30 0.35 0.29 0.45 7020002 17 32 0.33 0.27 0.42 7020003 18 27 0.34 0.28 0.48 7020004 19 24 0.30 0.21 0.46 7020005 20 27 0.30 0.22 0.42 7020006 21 24 0.34 0.27 0.50 7020007 22 26 0.34 0.27 0.52 7020008 23 23 0.29 0.19 0.48 7020009 24 26 0.30 0.23 0.47 7020010 25 25 0.37 0.30 0.49 7020011 26 26 0.30 0.23 0.45 7020012 27 24 0.27 0.18 0.45 7030001 28 48 0.28 0.22 0.35 7030002 29 48 0.26 0.20 0.34 7030003 30 45 0.29 0.23 0.36 7030004 31 49 0.26 0.21 0.33 7030005 32 42 0.26 0.18 0.35 7040001 33 39 0.31 0.25 0.38 7040002 34 30 0.27 0.18 0.40 7040003 35 41 0.25 0.18 0.36 7040004 36 33 0.25 0.17 0.42 7040005 37 33 0.26 0.17 0.39 7040006 38 37 0.29 0.22 0.39 7040007 39 36 0.25 0.14 0.34 7040008 40 31 0.24 0.16 0.40 7050001 41 44 0.26 0.19 0.34 7050002 42 48 0.29 0.23 0.34 7050003 43 49 0.31 0.24 0.36

    1‐29

  •                      

     

    Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    7050004 44 44 0.28 0.21 0.33 7050005 45 33 0.28 0.19 0.38 7050006 46 37 0.27 0.19 0.36 7050007 47 39 0.25 0.18 0.37 7060001 48 40 0.34 0.30 0.39 7060002 49 41 0.24 0.17 0.33 7060003 50 34 0.31 0.25 0.39 7060004 51 27 0.24 0.15 0.38 7060005 52 41 0.30 0.25 0.38 7060006 53 23 0.25 0.15 0.49 7070001 54 51 0.26 0.18 0.32 7070002 55 36 0.29 0.22 0.37 7070003 56 28 0.28 0.17 0.42 7070004 57 42 0.26 0.19 0.34 7070005 58 37 0.25 0.17 0.34 7070006 59 40 0.26 0.19 0.34 7080101 60 35 0.30 0.24 0.38 7080102 61 25 0.27 0.17 0.44 7080103 62 24 0.28 0.19 0.46 7080104 63 24 0.31 0.22 0.48 7080105 64 24 0.27 0.16 0.43 7080106 65 30 0.27 0.19 0.39 7080107 66 25 0.28 0.19 0.47 7080201 67 21 0.28 0.17 0.44 7080202 68 23 0.32 0.23 0.42 7080203 69 22 0.32 0.22 0.47 7080204 70 22 0.31 0.21 0.46 7080205 71 24 0.27 0.16 0.40 7080206 72 22 0.35 0.26 0.44 7080207 73 22 0.29 0.18 0.45 7080208 74 19 0.30 0.19 0.48 7080209 75 22 0.29 0.19 0.44 7090001 76 31 0.28 0.20 0.41 7090002 77 36 0.32 0.25 0.40 7090003 78 31 0.24 0.16 0.35 7090004 79 44 0.26 0.19 0.33 7090005 80 33 0.25 0.16 0.37 7090006 81 34 0.29 0.22 0.39 7090007 82 26 0.29 0.21 0.46 7100001 83 24 0.32 0.24 0.49 7100002 84 25 0.29 0.19 0.43 7100003 85 23 0.34 0.26 0.50 7100004 86 26 0.31 0.22 0.44 7100005 87 23 0.32 0.23 0.46 7100006 88 23 0.25 0.15 0.46 7100007 89 29 0.28 0.20 0.40 7100008 90 37 0.26 0.17 0.33 7100009 91 40 0.24 0.15 0.32 7110001 92 35 0.27 0.19 0.39 7110002 93 45 0.26 0.19 0.33

    1‐30

  •                      

     

    Delivery Ratio used in CEAP in the Upper Mississippi River Basin

    7110003 94 44 0.28 0.22 0.37 7110004 95 43 0.33 0.30 0.40 7110005 96 41 0.27 0.20 0.35 7110006 97 40 0.31 0.25 0.37 7110007 98 38 0.33 0.27 0.41 7110008 99 46 0.27 0.21 0.34 7110009 100 39 0.36 0.31 0.43 7120001 101 26 0.28 0.20 0.42 7120002 102 22 0.32 0.24 0.53 7120003 103 30 0.43 0.39 0.55 7120004 104 35 0.36 0.32 0.45 7120005 105 25 0.31 0.22 0.45 7120006 106 35 0.27 0.19 0.35 7120007 107 24 0.30 0.22 0.46 7130001 108 24 0.28 0.18 0.45 7130002 109 20 0.31 0.21 0.49 7130003 110 33 0.36 0.29 0.44 7130004 111 25 0.29 0.19 0.43 7130005 112 22 0.28 0.18 0.50 7130006 113 23 0.28 0.18 0.47 7130007 114 23 0.35 0.27 0.47 7130008 115 25 0.33 0.26 0.49 7130009 116 21 0.29 0.19 0.51 7130010 117 30 0.30 0.22 0.36 7130011 118 27 0.32 0.25 0.42 7130012 119 27 0.31 0.21 0.44 7140101 120 46 0.32 0.26 0.39 7140102 121 48 0.24 0.18 0.33 7140103 122 54 0.25 0.19 0.33 7140104 123 48 0.26 0.21 0.32 7140105 124 56 0.29 0.25 0.35 7140106 125 49 0.27 0.22 0.33 7140107 126 51 0.30 0.26 0.35 7140108 127 41 0.34 0.29 0.43 7140201 128 26 0.28 0.20 0.47 7140202 129 38 0.29 0.22 0.38 7140203 130 40 0.30 0.24 0.36 7140204 131 45 0.27 0.21 0.33

    1‐31

  • Delivery Ratio used in CEAP in the Upper Mississippi River Basin

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    Maner, S.B. 1958. Factors affecting sediment delivery rates in the Red Hills physiographic area. Trans. AGU , Vol. 39, No 4, pp. 669-675.

    Maner, S. B. 1962. Factors influencing sediment delivery ratios in the Blackland Prairie land resource area. USDA, SCS, Fort Worth, TX, 10pp.

    Mausbach, J.M., and A.R. Dedrick. 2004. The length we go: Measuring environmental benefits of conservation practices in the CEAP. J. Soil and Water Conserv. 59(5): 96A.

    Meade, R. H., T. Yuzyk, and T. Day. 1990. Movement and storage of sediment in rivers of the United States and Canada. Pp. 255-280 in The Geology of North America. W. H. Riggs (ed.). Geological Society of America. O-1. Chapter 11.

    Menzel, R. G. 1980. Enrichment ratios for water quality modeling. P. 486-492. In W. G. Knisel (ed.) CREAMS. A field scale model for chemicals, runoff and erosion from agricultural management systems. U.S. Dept. of Agric. Conserv. Res. Rept. Mo. 26.

    Mutua, B.M., A. Klik and W. Loiskandl. 2006. Modeling soil erosion and sediment yield at a catchment scale: The case of masinga catchment, Kenya. Land Degradation & Development. 17:557-570.

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    Morgan, R.P.C., Quinton, J.N., Smith, R.E., Govers, G., Poesen, J.W.A., Auerswald, K., Chisci, G., Torri, D., Styczen, M.E., 1998. The European Soil Erosion Model (EUROSEM): a dynamic approach for predicting sediment transport form fields and small catchments. Earth Surface Processes & Landforms 23: 527-544.

    Neitsch, S. L., J. G. Arnold, J. R. Kiniry, and J. R. Williams. 2005. Soil and Water Assessment Tool (Version 2005). Theoretical documentation. Grassland, Soil and Water Research Laboratory, USDA-ARS, Temple, TX 76502 and Blackland Research Center, Temple, TX 76502.

    Ouyang, D. and J. Bartholic. 1997. Predicting sediment delivery ratio in Saginaw Bay Watershed. In The 22nd National Association of Environmental Professionals Conference Proceedings. May 19-23, 1997, Orlando, FL. pp 659-671.

    Pannell, R. 1999. Sediment response to large-scale environmental change: the Upper Mississippi River, 1943-1996. M.S. Thesis. University of Wisconsin-Madison.

    Roehl, J.W. 1962. Sediment source areas, delivery ratios, and influencing morphological factors. In Land Erosion, IAHS Publ. No. 59, pp 202-213.

    Santhi, C., Kannan, N., Di Luzio, M., Potter, S.R., Arnold, J.G., Atwood, J.D., and Kellogg, R.L. 2005. An approach for estimating water quality benefits of conservation practices at the national level. In American Society of Agricultural and Biological Engineers (ASABE), Annual International Meeting, Tampa, Florida, USA, July 17–20, 2005 (Paper Number: 052043).

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    Williams, J.R. 1975b. Sediment routing for agricultural watersheds. Water Resour. Bull. 11(5), 965-974.

    Williams, J.R. 1977. Sediment delivery ratios determined with sediment and runoff models. In: Erosion and Solid Matter Transport in Inland Waters, IAHS-AISH, Publ. No. 122, pp. 168-179.

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    Williams, J.R. and H.D. Berndt. 1972. Sediment yield computed with Universal Equation. Journal of the Hydraulics Div., ASCE, Vol. 98, No HY12, pp. 2087-2098.

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    1-33

  • Chapter 2

    Delivery Ratio used in CEAP Cropland

    Modeling in the Chesapeake Bay

    Watershed

    2-1

  • Delivery Ratio used in CEAP in the Chesapeake Bay Watershed

    The APEX model is a field-scale, daily time-step model that simulates weather, farming operations, crop growth and yield, and the movement of water, soil, carbon, nu-trients, sediment, and pesticides. The APEX model was used also to simulate the effects of conservation practices at the field scale (Williams and Izaurralde, 2006; Gassman et al. 2009) in the Chesapeake Bay Watershed. APEX si-mulates all of the basic biological, chemical, hydrological, and meteorological processes of farming systems and their interactions. Soil erosion is simulated over time, including wind, sheet and rill erosion. The nitrogen, phosphorus, and carbon cycles are simulated, including chemical transfor-mations in the soil that affect their availability for plant growth or for transport from the field.

    While the APEX model was used to simulate the culti-vated cropland and the SWAT model was used to simulate the non-cultivated cropland in the 8-digit watersheds (sub-basins) of the river basin. SWAT is a physical process model with a daily time step (Arnold and Fohrer 2005; Arnold et al. 1998; Gassman et al. 2007). The hydrologic cycle in the model is divided into two parts. The land phase of the hydrologic cycle, or upland processes, simu-lates the amount of water, sediment, nutrients, and pesti-cides delivered from the land to the outlet of each wa-tershed. The routing phase of the hydrologic cycle, or channel processes, simulates the movement of water, se-diment, nutrients, and pesticides from the outlet of the up-stream watershed through the main channel network to the watershed outlet.

    In SWAT, each 8-digit watershed is divided into multiple Hydrologic Response Units (HRUs) that have homogene-ous land use, soil and slope. SWAT is used to simulate the fate and transport of water, sediment, nutrients, and pesti-cides from various non-cropland HRUs as described in Chapter 1.

    Not all of the soil that erodes from a field or HRUs ends up in the watershed outlet. Most of the soil eroded gets deposited on the way although the deposition is temporary. Eroded soil may deposit in low spots, flatr lands, at the edge of the field and sometimes settles at the bottom of the channel. Hence, a SDR was used to account for deposition in ditches, floodplains, and tributary stream channels dur-ing transit from the edge of the field or HRUs to the 8-digit watershed outlet in the CEAP National Assessment model-ing. The SDR used in this study is a function of the ratio of the time of concentration for the HRU (land uses other than cultivated cropland) or field (cultivated cropland) to the time of concentration for the watershed (8-digit HUC).

    The time of concentration for the watershed is the time from when a surface water runoff event occurs at the most distant point in the watershed to the time the surface water runoff reaches the outlet of the watershed. It is calculated by summing the overland flow time (the time it takes for flow from the remotest point in the watershed to reach the channel) and the channel flow time (the time it takes for flow in the upstream channels to reach the outlet). The time of concentration for the field is derived from APEX. The time of concentration for the HRU is derived from characteristics of the watershed, the HRU, and the propor-tion of total acres represented by the HRU. Consequently, each cultivated cropland sample point has a unique deli-very ratio within each watershed, as does each HRU. The description of the SDR procedure is provided in Chapter 1.

    The APEX model simulates the edge of sediment yield using a variation of MUSLE called MUST (MUSLE de-veloped from Theory) (Williams 1995) as described in Chapter 1. After estimating the sediment load from each APEX simulation site, the delivery ratio is applied to de-termine the amount of sediment that reaches the 8-digit watershed outlet from each APEX simulation site. The sediment load from APEX simulation sites are aggregated for the 8-digit watershed and integrated into the SWAT model at each 8-digit watershed to estimate the water qual-ity effects of conservation practices. In SWAT, the sedi-ment yield for the non-cropland HRUs are estimated using the MUSLE as described in Chapter 1. After estimating the SDR for each HRU, the SDR is applied to determine the amount of sediment that reaches the 8-digit watershed out-let.

    Sediment delivery ratios were estimated to account for sediment losses or deposition occurring from edge-of-field or HRUs to the 8-digit watershed outlet for each APEX simulation site in the cultivated cropland and CRP and non-cropland HRUs in the Chesapeake Bay Watershed (Figure 2-1). The Chesapeake Bay has a drainage area of 43.85 million acres. The cultivated cropland and land enrolled in the CRP General Signup is about 10 percent of the Chesapeake Bay Watershed. A total of 58 8-digit wa-tersheds are in the Chesapeake Bay Watershed (Figure 2-1). Within each 8-digit watershed, the percent of cultivated cropland and CRP area and non-cultivated cropland area varies widely across the entire watershed.

    A total of 832 representative cultivated fields (771 NRI-CEAP cropland points and 61 CRP points) were setup to run using APEX. Eight out of 57, 8-digit watersheds in the Chesapeake Bay Watershed have no CEAP points.

    2-2

  • Delivery Ratio used in CEAP in the Chesapeake Bay Watershed

    These 8-digit watersheds have zero or fewer than 6% per-centage cultivated cropland.

    Non-cultivated land is distributed over 90 percent of the Chesapeake Bay Watershed. Within each 8-digit wa-tershed, non-cultivated land uses such as pasture, range, hay, horticulture, forest deciduous, forest mixed, forest evergreen, urban, urban construction, barren land wetland and water are simulated as HRUs in SWAT. A total of 2598 HRUs are simulated in SWAT for the Chesapeake Bay Watershed.

    Each NRI-CEAP point and CRP point is unique; therefore, sediment yield and delivery ratio also vary for each culti-vated cropland site simulated in an 8-digit watershed as well as for HRU. The number of CEAP sample points, and mean, 10th percentile and 90th percentile of the delivery ratios of the APEX simulation sites in the 8-digit water-sheds in the Chesapeake Bay are shown in Table 2-1 and Figure 2-1. Table 2-2 shows the number of HRUs and mean, 10th percentile and 90th percentile of the SDRs es-timated for the non-cultivated land HRUs in the 8-digit watersheds in the Chesapeake Bay Watershed (Figure 2-1). The mean, 10th and 90th percentile SDRs for the non-cropland HRUs are depicted in Figure 2-2.

    In addition to the SDR, an enrichment ratio was used to simulate organic nitrogen, organic phosphorus, and sedi-ment-attached pesticide transport in ditches, floodplains, and tributary stream channels during transit from the edge-of-field to the outlet. The enrichment ratio was defined as the organic nitrogen, organic phosphorus, and sediment attached pesticide concentration from the edge-of-field divided by the concentration at the 8-digit watershed outlet as dicussed in Chapter 1. The enrichment ratio is esti-mated for each APEX simulation site and SWAT HRU and it varies from 0.5 to 1.5 (average=1). As sediment is transported from the edge-of-field to the watershed outlet, coarse sediments are deposited first while more of the fine sediment that hold organic particles remain in suspension, thus enriching the organic concentrations delivered to the watershed outlet.

    A separate delivery ratio is used to simulate the transport of nitrate-nitrogen, soluble phosphorus, and soluble pesti-cides. In general, the proportion of soluble nutrients and pesticides delivered to rivers and streams is higher than the proportion attached to sediments because they are not sub-ject to sediment deposition.

    2-3

  • Figure 2-1 Map of the 8-digit watersheds in the Chesapeake Bay Watershed

    3-1

  • Table 2-1. Mean and percentiles of sediment delivery ratio (sediment delivered at 8-digit watershed outlet by sediment yield at simulation sites) estimated for cultivated simulation sites within APEX for the 8-digit watersheds in the Chesapeake Bay Watershed

    HUC Cropland CRP Crop + CRP Point

    s Mean

    SDR

    Point s

    Mean

    SDR

    Point s

    Mean_S DR

    10th percen-tile SDR

    90th per-centile SDR

    2050101 3 0.32 3 0.32 0.31 0.35 2050102 4 0.36 2 0.33 6 0.35 0.31 0.44 2050103 1 0.42 1 0.42 0.42 0.42 2050104 4 0.39 4 0.39 0.35 0.44 2050105 4 0.44 3 0.38 7 0.42 0.37 0.53 2050106 4 0.37 6 0.34 10 0.35 0.33 0.38 2050107 7 0.37 7 0.35 14 0.36 0.32 0.44 2050201 1 0.33 1 0.33 0.33 0.33 2050203 1 0.39 1 0.39 0.39 0.39 2050204 3 0.46 1 0.39 4 0.44 0.39 0.54 2050205 2 0.39 2 0.39 0.38 0.40 2050206 15 0.37 2 0.34 17 0.36 0.33 0.41 2050301 21 0.37 2 0.34 23 0.37 0.34 0.41 2050302 3 0.47 1 0.39 4 0.45 0.39 0.56 2050303 3 0.38 3 0.38 0.36 0.40 2050304 9 0.35 2 0.32 11 0.34 0.31 0.42 2050305 38 0.38 2 0.35 38 0.38 0.36 0.41 2050306 92 0.34 94 0.34 0.32 0.38 2060002 57 0.44 9 0.40 66 0.43 0.39 0.50 2060003 24 0.41 24 0.41 0.37 0.50 2060004 2 0.46 2 0.46 0.46 0.46 2060005 53 0.44 3 0.42 56 0.44 0.38 0.50 2060006 20 0.35 20 0.35 0.31 0.42 2060007 12 0.49 1 0.46 13 0.49 0.44 0.58 2060008 57 0.45 1 0.37 58 0.45 0.39 0.49 2060009 30 0.42 30 0.42 0.40 0.48 2060010 23 0.53 1 0.51 24 0.53 0.46 0.58 2070001 4 0.42 4 0.42 0.39 0.49 2070002 1 0.40 1 0.40 0.40 0.40 2070003 1 0.37 1 0.21 2 0.29 0.21 0.37 2070004 36 0.35 1 0.34 37 0.35 0.33 0.37 2070005 9 0.36 9 0.36 0.34 0.40 2070006 3 0.38 3 0.38 0.38 0.39 2070007 6 0.45 6 0.45 0.41 0.55 2070008 15 0.39 4 0.33 19 0.38 0.35 0.48 2070009 38 0.40 1 0.42 39 0.40 0.37 0.42 2070010 4 0.38 4 0.38 0.36 0.41 2070011 25 0.41 2 0.31 27 0.40 0.37 0.44 2080102 21 0.47 1 0.32 22 0.47 0.42 0.54 2080103 7 0.42 1 0.30 8 0.40 0.30 0.47 2080104 25 0.37 3 0.21 28 0.35 0.24 0.40

    3-2

  • Sedi

    men

    t Del

    iver

    y R

    atio

    0.7

    0.6

    0.5

    0.4

    0.3

    0.2

    0.1

    0.0

    2080105 16 0.39 1 0.22 17 0.38 0.32 0.41 2080106 8 0.40 8 0.40 0.35 0.48 2080107 3 0.46 3 0.46 0.45 0.49 2080109 17 0.61 17 0.61 0.54 0.71 2080110 13 0.55 13 0.55 0.48 0.63 2080206 15 0.43 2 0.25 17 0.41 0.25 0.53 2080207 2 0.36 1 0.21 3 0.31 0.21 0.38 2080208 9 0.47 9 0.47 0.43 0.54

    Figure 2-2. Mean and percentiles of sediment delivery ratio (sediment delivered at 8-digit watershed out-let by sediment yield at simulation sites) estimated for cultivated simulation sites within APEX for the 8-digit watersheds in the Chesapeake Bay Watershed

    Chesapeake Bay Watershed

    0.8 Mean SDR 10th Percentile SDR 90th Percentile SDR

    2050

    101

    2050

    103

    2050

    105

    2050

    107

    2050

    203

    2050

    205

    2050

    301

    2050

    303

    2050

    305

    2060

    002

    2060

    004

    2060

    006

    2060

    008

    2060

    010

    2070

    002

    2070

    004

    2070

    006

    2070

    008

    2070

    010

    2080

    102

    2080

    104

    2080

    106

    2080

    109

    2080

    206

    2080

    208

    HUC8

    3-3

  • Table 2-3. Mean and percentiles of sediment delivery ratio (sediment delivered at 8-digit watershed outlet by sediment yield at HRUs) estimated for non-cultivated land HRUs within SWAT for the 8-digit water-sheds in the Chesapeake Bay Watershed

    HUC Subbasin Number of non-cropland HRUs

    simulated within SWAT

    Mean SDR 10th Percen-tile

    SDR

    90th Percentile SDR

    2050101 1 53 0.18 0.13 0.31 2050102 2 50 0.21 0.15 0.27 2050103 3 54 0.23 0.19 0.29 2050104 4 50 0.24 0.19 0.30 2050105 5 43 0.25 0.19 0.31 2050106 6 49 0.22 0.15 0.29 2050107 7 43 0.23 0.16 0.32 2050201 8 40 0.22 0.14 0.33 2050202 9 31 0.27 0.18 0.38 2050203 10 33 0.24 0.15 0.37 2050204 11 31 0.27 0.19 0.42 2050205 12 34 0.26 0.18 0.36 2050206 13 47 0.22 0.15 0.29 2050301 14 41 0.23 0.17 0.34 2050302 15 27 0.30 0.22 0.40 2050303 16 42 0.22 0.15 0.31 2050304 17 37 0.22 0.11 0.33 2050305 18 51 0.24 0.19 0.30 2050306 19 61 0.22 0.19 0.27 2060001 20 21 0.42 0.35 0.50 2060002 21 36 0.32 0.23 0.43 2060003 22 58 0.26 0.23 0.32 2060004 23 33 0.36 0.31 0.43 2060005 24 38 0.31 0.23 0.41 2060006 25 52 0.21 0.15 0.28 2060007 26 35 0.42 0.34 0.50 2060008 27 33 0.32 0.25 0.43 2060009 28 41 0.30 0.24 0.35 2060010 29 40 0.25 0.18 0.32 2070001 30 38 0.24 0.16 0.34 2070002 31 38 0.25 0.19 0.33 2070003 32 42 0.23 0.16 0.34 2070004 33 58 0.22 0.17 0.30 2070005 34 71 0.20 0.15 0.27 2070006 35 60 0.24 0.19 0.31 2070007 36 34 0.31 0.24 0.35 2070008 37 76 0.24 0.19 0.28 2070009 38 73 0.25 0.21 0.29 2070010 39 61 0.26 0.21 0.29 2070011 40 48 0.30 0.26 0.35 2080102 41 48 0.40 0.35 0.50

    3-4

  • Sedi

    men

    t Del

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    atio

    0.7

    0.6

    0.5

    0.4

    0.3

    0.2

    0.1

    0.0

    2080103 42 61 0.28 0.23 0.32 2080104 43 47 0.25 0.19 0.33 2080105 44 49 0.26 0.22 0.31 2080106 45 56 0.27 0.22 0.31 2080107 46 33 0.39 0.34 0.46 2080108 47 28 0.52 0.45 0.61 2080109 48 26 0.57 0.53 0.64 2080110 49 40 0.26 0.19 0.35 2080201 50 48 0.21 0.13 0.29 2080202 51 47 0.24 0.19 0.32 2080203 52 61 0.21 0.16 0.27 2080204 53 57 0.24 0.19 0.30 2080205 54 50 0.28 0.24 0.32 2080206 55 51 0.33 0.28 0.39 2080207 56 54 0.25 0.20 0.30 2080208 57 39 0.36 0.32 0.41

    Figure 2-2. Mean and percentiles of sediment delivery ratio (sediment delivered at 8-digit watershed out-let by sediment yield at HRUs) estimated for non-cultivated land HRUs within SWAT for the 8-digit wa-tersheds in the Chesapeake Bay Watershed

    Chesapeake Bay Watershed

    0.8 Mean SDR 10th Percentile SDR 90th Percentile SDR

    2050

    101

    2050

    103

    2050

    105

    2050

    107

    2050

    202

    2050

    204

    2050

    206

    2050

    302

    2050

    304

    2050

    306

    2060

    002

    2060

    004

    2060

    006

    2060

    008

    2060

    010

    2070

    002

    2070

    004

    2070

    006

    2070

    008

    2070

    010

    2080

    102

    2080

    104

    2080

    106

    2080

    108

    2080

    110

    2080

    202

    2080

    204

    2080

    206

    2080

    208

    HUC8

    3-5

  • Chapter 3

    Delivery Ratio used in CEAP Cropland

    Modeling in the Delaware River Basin

    3-6

  • The APEX model is a field-scale, daily time-step model that simulates weather, farming operations, crop growth and yield, and the movement of water, soil, carbon, nutrients, sediment, and pesticides. The APEX model was used also to simulate the effects of conservation practices at the field scale (Williams and Izaurralde, 2006; Gassman et al. 2009) in the Dela-ware River Basin. APEX simulates all of the basic biological, chemical, hydrological, and meteorologi-cal processes of farming systems and their interac-tions. Soil erosion is simulated over time, including wind, sheet and rill erosion. The nitrogen, phospho-rus, and carbon cycles are simulated, including chem-ical transformations in the soil that affect their availa-bility for plant growth or for transport from the field.

    While the APEX model was used to simulate the cultivated cropland, the SWAT model was used to simulate the non-cultivated cropland in the 8-digit watersheds of the river basin. SWAT is a physical process model with a daily time step (Arnold and Fohrer 2005; Arnold et al. 1998; Gassman et al. 2007). The hydrologic cycle in the model is divided into two parts. The land phase of the hydrologic cycle, or upland processes, simulates the amount of water, sediment, nutrients, and pesticides delivered from the land to the outlet of each watershed. The routing phase of the hydrologic cycle, or channel processes, simulates the movement of water, sedi-ment, nutrients, and pesticides from the outlet of the upstream watershed through the main channel net-work to the watershed outlet.

    In SWAT, each 8-digit watershed is divided into mul-tiple Hydrologic Response Units (HRUs) that have homogeneous land use, soil, and slope. SWAT is used to simulate the fate and transport of water, sedi-ment, nutrients, and pesticides from various non-cropland HRUs as described in Chapter 1.

    Not all of the soil that erodes from a field or HRUs ends up in the watershed outlet. Most of the soil eroded gets deposited on the way although the depo-sition is temporary. Eroded soil may deposit in lower spots, flatter lands, deposited at the edge of the field and sometimes settles at the bottom of the channel. Hence, a SDR was used to account for deposition in ditches, floodplains, and tributary stream channels during transit from the edge of the field or HRUs to the 8-digit watershed outlet in the CEAP National Assessment modeling. The SDR used in this study is a function of the ratio of the time of concentration for the HRU (land uses other than cultivated cropland) or

    field (cultivated cropland) to the time of concentra-tion for the watershed (8-digit HUC). The time of concentration for the watershed is the time from when a surface water runoff event occurs at the most distant point in the watershed to the time the surface water runoff reaches the outlet of the watershed. It is calcu-lated by summing the overland flow time (the time it takes for flow from the remotest point in the wa-tershed to reach the channel) and the channel flow time (the time it takes for flow in the upstream chan-nels to reach the outlet). The time of concentration for the field is derived from APEX. The time of concen-tration for the HRU is derived from characteristics of the watershed, the HRU, and the proportion of total acres represented by the HRU. Consequently, each cultivated cropland sample point has a unique deli-very ratio within each watershed, as does each HRU. The description of the SDR procedure is provided in Chapter 1.

    The APEX model simulates the edge of sediment yield using a variation of MUSLE called MUST (MUSLE developed from Theory) (Williams 1995) as described in Chapter 1. After estimating the sediment load from each APEX simulation site, the delivery ratio is applied to determine the amount of sediment that reach the 8-digit watershed outlet from each APEX simulation site. The sediment load from apex simulation sites are aggregated for the 8-digit wa-tershed and integrated into the SWAT model at each 8-digit watershed to estimate the water quality effects of conservation practices. In SWAT, the sediment yield for the non-cropland HRUs are estimated using the MUSLE as described in Chapter 1. After estimat-ing the SDR for each HRU, the SDR is applied to determine the amount of sediment that reach the 8-digit watershed outlet.

    Sediment delivery ratios were estimated to account for sediment losses or deposition occurring from edge-of-field or HRUs to the 8-digit watershed outlet for each APEX simulation site in the cultivated crop-land and CRP and non-cropland HRUs in the Dela-ware River Basin (Figure 3-1). The Delaware River Basin has a drainage area of 8.72 million acres. The cultivated cropland and land enrolled in the CRP General Signup is about 13 percent of the Delaware River Basin. A total of 13, 8-digit watersheds are in the Delaware River Basin (Figure 3-1). Within each 8-digit watershed, the percent of cultivated cropland and CRP area and non-cultivated cropland area varies widely across the entire watershed.

    3-7

  • Delivery Ratio used in CEAP in the Delaware River Basin

    A total of 188 representative cultivated fields (186 NRI-CEAP cropland points and 2 CRP points) were setup to run using APEX. Four out of 14, 8-digit wa-tersheds in the Delaware River Basin have no CEAP points. The non-cultivated land is distributed over 87 percent of the Chesapeake Bay Watershed. Within each 8-digit watershed, non-cultivated land uses such as pasture, range, hay, horticulture, forest deciduous, forest mixed, forest evergreen, urban, urban construc-tion, barren land wetland and water are simulated as HRUs in SWAT. A total of 501 HRUs are simulated in SWAT for the Delaware River Basin.

    Each NRI-CEAP point and CRP point is unique; therefore, sediment yield and delivery ratio also vary for each cultivated cropland site simulated in an 8-digit watershed and so as for HRU. The number of CEAP sample points,